This invention concerns apparatus for improving the signal-to-noise characteristic of side panel information relative to center panel information in a widescreen television-type signal processing system.
U.S. Pat. No. 4,816,899--Strolle et al. discloses a widescreen television signal processing system wherein low frequency left and right side panel information, exclusive of high frequency side panel information, is encoded by time compressing such information into left and right horizontal image overscan regions. Specifically, in the case of the luminance signal, luminance information from DC to 700 KHz is time compressed approximately 6:1, resulting in a bandwidth of approximately 4.2 MHz. The receiver performs a complementary time expansion.
Because of the time compression and expansion during the encoding and decoding processes, the side panel low frequency component contains much more noise energy under noisy channel conditions than the same low frequency band of center panel information. This condition manifests itself as an objectionable difference in the noise characteristics of displayed center panel and side panel images. Specifically, side panel images exhibit horizontally "streaky" low frequency noise which contrasts with the broader bandwidth noise in the center panel image and which is more objectionable. Side panel information therefore appears visibly different from center panel information, particularly for transmission channels with signal-to-noise ratios below about 35 db.